Bobbin thread depletion detector for sewing machines



E. H. DOERNER April 21, 1964 BOBBIN THREAD DEPLETION DETECTOR FOR SEWINGMACHINES 2 Sheets-Sheet Filed May 23, 1962 R E R M Y O E T. E N m w R wm 1 T H A H Y E m WL E y W n n m W P mm 0 m 0 m Y.-. 2 Y m y E I -UI T FW l. .WWMHIMHUHFIJLHIMWMW m x 5 .Il 4

April 21, 1964 DOERNER 3,129,680

BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES Filed May 23, 19622 Sheets-Sheet 2 Fig. 7 43 INVENTOR. ERNEST H. DOERNER 4. 49 WW E!ATTORNEY United States Patent 3,129,680 BOBBIN THREAD DEPLETION DETECTORFOR SEWING MACHINES Ernest H. Doerner, Morris Plains, N.J., assignor toThe Singer Company, a corporation of New Jersey Filed May 23, 1962, Ser.No. 197,151 4 Claims. (Cl. 112-218) This invention relates to a bobbindepletion detector for sewing machines.

It is desirable in sewing machines, particularly of the lock stitchtype, for the operator to know in advance when the bobbin thread isabout to run out so she can complete the sewing to the next logicalstopping point and rewind the bobbin. In this manner unsuspectedrun-outs can be avoided and the general quality of the work improved byeliminating the necessity of restitching over paths already perforatedby the needle.

It is an object of this invention to provide a sewing machine with meansfor indicating to the operator that the bobbin thread is nearlydepleted. I

It is a more specific object of this invention to provide on the bobbinof a sewing machine magnetic means movable in response to near-depletionof the thread wound thereon to a position in which its field influencesa magnetic-reed switch to closure to provide a signal to the operatorthat bobbin thread exhaustion is imminent.

With the above and other objects in view, as will hereinafter appear,the invention comprises the devices, combinations and arrangements ofparts hereinafter set forth and illustrated in the accompanying drawingsof a preferred embodiment of the invention, from which the severalfeatures of the inveniton and the advantages attained thereby will bereadily understood by those skilled in the art.

In the drawings, FIG. 1 is a front elevation view partly in section of aportion of a sewing machine embodying the invention.

FIG. 2 is a top plan view of the devices of FIG. 1.

FIG. 3 is a vertical sectional view taken on line 3-3 of FIG. 2.

FIG. 4 is a vertical sectional View taken substantially on line 44 ofFIG. 2, and includes a schematic wiring diagram.

FlG. 5 is a bottom plan detail view partly in section of a bobbinembodying the invention.

FIG. 6 is a sectional view taken on line 6-6 of FIG. 5.

FIG. 7 is a view similar to FIG. 4 showing a modification of theinvention.

As illustrated in the drawings, the present invention is shown embodiedin a sewing machine of the type shown and described in United StatesPatent No. 2,862,- 468, dated December 2, 1958, to which reference maybe had for a complete understanding of the operation thereof.

Referring now to FIG. 1 there is shown a portion of a sewing machinehaving a base 10 with vertical end wall 11, and a head 12 carrying aneedle bar 13, needle 14, presser bar 15, presser-foot 16 and feed-dog16a.

A bed shaft 17 drives a hook shaft 18 through bevel gears 19 and 20 toimpart rotary movement to a hook 21. A bobbin 22 is shown seated withina bobbin carrier 23 in its relation to the rotary hook 21. A removableslide plate 24 covers the rotary hook mechanism and may be readilypulled back to gain access for bobbin removal and replacement as is wellknown.

Secured to the end wall 11 by any suitable means, such as screw 25, is amolded plastic block 26 in which is embedded a magnetic reed switch 27of conventional type and a permanent magnet 28 shown best in properrelative position in FIGS. 2 and 3. The reed switch has ice conductingleads 29 and 30 for external connections to be described later. Thepermanent magnet 28 is magnetized along its axis with its terminal endsproviding poles of opposite polarity as shown by the plus and minussigns. The magnet 28 is positioned and aligned with respect to the reedswitch 27 to provide a constant magnetic flux field tending to close butnot actually closing the reed contacts of the switch 27. That is to say,the magnet 82 provides a biasing magnetic field for the reed switchwhich requires a slight but definite additional field of the samepolarity as the magnet 28 to cause closure of the reed switch 27.Further, the field created by the magnet 28 is suflicient, by itself, tohold the reed switch closed (when once closed) even when said additionalfield is removed. This is known as latch action. By the same token, whenthe reed switch is closed and the additional field is removed, itrequires a small but definite subtractive field of opposite polarity toopen the reed switch. How these additional and subtractive fields of therespective same and opposite polarity are provided will now bedescribed.

The additional field of the same polarity as the biasing magnet 23 issupplied by the proximity effect of a permanent magnet 31 carried by thebobbin 22 as shown best in FIGS. 5 and 6, the bobbin 22, formed fromnonmagnetic material such as aluminum, has its lower flange 33 formedwith an internal annular groove 34 within which is seated a circularwire snap-ring 35. One end of the snap-ring 35 embraces a grooved end 36of the magnet 31 which is slidable within radial slots 37 and 38 in theflanges of the bobbin 22. Normally the flexure of the snap-ring 35biases the magnet 31 to the radially outward position shown in fulllines in FIG. 5 and in dotted lines in FIG. 6. However, when sufficientthread 39 is wound on the bobbin 22, the magnet 31 is forced to aposition against the hub portion 40 as shown in full lines in FIG. 6with the snap-ring 35 flexed as shown in dotted lines in FIG. 5.

From the above it will be perceived that, during the normal course ofsewing as thread 39 is pulled from the bobbin 22, it will rotate andwith it will carry the magnet 31 in a small circular path close to thehub axis. In this limited path (see FIG. 2) the magnet 31 never getsclose enough to the reed switch 27 to add suflicient field flux to thatsupplied by the biasing magnet 28 to cause closure of the reed switch27. However, when the bobbin thread supply becomes depleted the flexedspring 35 will overcome the snubbing action of the few remaining turnsof thread 39 and the magnet 31 will move to its outer radial positionand in its first turn past its nearest position to the reed switch 27will add suflicient magnetic flux to the field of the biasing magnet 28to cause closure of the reed switch 27 which, according to the latchaction described above, will remain closed even when the bobbin magnet31 moves away from the proximity position as the bobbin rotates.

As shown in the wiring diagram of FIG. 4, closure of the reed switch 27applies voltage from source 8-5 to a pilot lamp 41 located in a bracket42 secured to the head 12 thus lighting the lamp 41 and signalling tothe operator that the bobbin thread is about to run out. Lamp 43connected to the source SS is the lamp conventionally used to illuminatethe sewing area and is included here merely to show that the presentlyexisting voltage supply source SS can also be used for the pilot lamp41.

It is necessary to reset the reed switch 27 to open position and-it isdesirable that this be done by a normal operating function connectedwith bobbin replacement, such, for example, as movement of the slideplate. For this purpose a small permanent magnet 44 is secured to theunder side of the slide plate 24 and is so located (FIG. 2) that, as theplate is pulled out and/or pushed in it will traverse a position closeto the reed switch 27. It will be understood that the polarity of thereset magnet 44 is related to that of the biasing magnet 28 such that itexerts a sufficiently subtractive elfect on the biasing field flux toopen the reed switch. As a result, when a wound bobbin is inserted, thebobbin magnet 31 is out of the field of influence as regards the reedswitch 27 so that, when the slide plate 24 is pushed in, the resetmagnet takes control and opens the reed switch which is then reset andready for the next signal actuation.

Due to manufacturing tolerances, particularly related to the relativestrength of the various magnets, 28, 31, and 44, some adjustability isdesirable so that a final setting can be made to secure the desiredlatching action. This may be provided by a vertically elongated slot 45formed in the wall 11 which permits adjustment of the vertical positionof the reed switch 27 with respect to magnets 31 and 44.

It may also be desirable to provide independent adjustment of thebiasing magnet 28 and the modification of FIG. 7 may be used for thispurpose. In'this case the biasing magnet 28 is held in a well 46 formedin the block 26 between a non-magnetic bottoming spring 47 and anonmagnetic adjusting screw 48 threaded into the well 46. The screw 48is readily accessible by pushing back the slide plate 24.

In order best to control the flux path influencing the proper poerationof the reed switch 27, the slide plate 24, bobbin 22 and bobbin carrier23 are all preferably made of non-magnetic material such as aluminum.

Having thus set forth the nature of my invention what I claim herein is:

l. A bobbin thread depletion detector for sewing machines comprising abobbin, a magnetic reed switch mounted adjacent to said bobbin, abiasing magnet mounted in fixed relation to said switch and providing aflux field for said switch sufiicient to hold it closed, if closed, butinsufficient to close it, it open, a magnet rotatable with said bobbinand normally restrained in a first path in which it has no operativeeffect on said swtich but movable responsively to near-exhaustion ofsaid bobbin thread supply to a second path in which it causes closure ofsaid switch, and a reset magnet movable to a position adjacent said reedswitch and of such polarity as to oppose the holding field of thebiasing magnet and effect opening of said reed switch.

2. Apparatus according to claim 1 in which the biasing magnet isselectively adjustable in its position relatively to the reed switch.

3. Apparatus according to claim 1 in which the reed switch and biasingmagnet are adjustable as a unit in its position relatively to saidbobbin magnet.

4. A bobbin thread depletion detector for sewing machines comprising abobbin, a permanent magnet normally held by the thread wound on thebobbin to a first position closely adjacent to the bobbin axis andmovable to a second position radially outwardly from said first positionresponsively to near-exhaustion of the bobbin thread supply, a magneticreed switch mounted adjacent to said bobbin, a biasing magnet mountedadjacent to said reed switch, said bobbin magnet and said biasing magnetbeing so polarized that their combined magnetic effect is additive andelfects closure of said reed switch in the second position of the bobbinmagnet, a slide plate covering said bobbin, and a reset magnet mountedon said slide plate and movable therewith to a position adjacent to saidreed switch, said biasing magnet and said reset magnet being sopolarized that their combined magnetic elfect is subtractive and effectsopening of said reed switch when said slide plate is moved to gainaccess for bobbin replacement.

References Cited in the file of this patent UNITED STATES PATENTS2,760,024 Tunstall Aug. 21, 1956 2,877,361 Chase Mar. 10, 1959 3,043,931Gruber July 10, 1962

1. A BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES COMPRISING ABOBBIN, A MAGNETIC REED SWITCH MOUNTED ADJACENT TO SAID BOBBIN, ABIASING MAGNET MOUNTED IN FIXED RELATION TO SAID SWITCH AND PROVIDING AFLUX FIELD FOR SAID SWITCH SUFFICIENT TO HOLD IT CLOSED, IF CLOSED, BUTINSUFFICIENT TO CLOSE IT, IF OPEN, A MAGNET ROTATABLE WITH SAID BOBBINAND NORMALLY RESTRAINED IN A FIRST PATH IN WHICH IT HAS NO OPERATIVEEFFECT ON SAID SWITCH BUT MOVABLE RESPONSIVELY TO NEAR-EXHAUSTION OFSAID BOBBIN THREAD SUPPLY TO A SECOND PATH IN WHICH IT CAUSES CLOSURE OFSAID SWITCH, AND A RESET MAGNET MOVABLE TO A POSITION ADJACENT SAID REEDSWITCH AND OF SUCH POLARITY AS TO OPPOSE THE HOLDING FIELD OF THEBIASING MAGNET AND EFFECT OPENING OF SAID REED SWITCH.